This invention relates generally to a thermal flow meter, and more particularly to a thermal flow meter which is suitable for measuring the quantity of intake air in an internal combustion engine.
As a thermal flow meter of the kind described above, a flow meter in which a temperature-dependent resistor made of a material such as platinum is disposed inside an air intake pipe has been known in the past (e.g. U.S. Pat. No. 3,747,577). Negative feedback control is effected so that the temperature-dependent resistor is kept at a constant temperature. The quantity of heat lost from the temperature-dependent resistor changes with changes in the intake air quantity, but since feedback control is effected so that its temperature remains constant, the intake air quantity can be measured by measuring the value of the current flowing through the resistor. However, the prior art device has the problem that its measurement accuracy is low.